Currently, prepared structural composite bonding surfaces which are intended for structural bonding with another material are not certifiable prior to bonding. Thus, much expense may be wasted in scraps due to the poor bonding quality of bonding surfaces on composites. Conventional design and maintenance practices may not solely rely on the performance of a bonded joint or repair on composites for structural certification. As bonded composite structures become more common as a way to reduce weight and improve airframe performance in modern aircraft, reliable methods may be required to directly certify the quality of the bonded joints between composites without adding additional contaminants that may negate their structural benefits. In addition, the use of structural bonding repair techniques, compared to mechanically-fastened joints, may become more viable as a long-term repair solution. Like composite bonded structures, bonded repairs may require a certification method to ensure the structural quality of the bonding surfaces which form the bond between composites.
One current solution for ensuring that an optimum structural bond surface exists on a composite structure may rely on tight process controls and skill of technicians to ensure quality and consistency. In some cases, cleanliness and roughness of the bonding surface may be measured and compared to an acceptable range to provide an inline process check. However, none of the known available methods can quantify and certify the bonding surface itself prior to structural bonding. Such a certification method would create confidence in the long-term durability of the bonded joint between composites after the structure which includes the bonded joint enters service. Individual surface characterization techniques that provide information on a single surface variable, such as surface roughness or active contaminants via profilometry or X-ray photoelectron spectroscopy (XPS), respectively, exist. However, both profilometry and XPS typical data may not quantify the structural bonding surface in terms of readiness to meet long-term structural joint durability, static strength and damage tolerance capability.
Conventional methods may not provide quantifiable engineering data related to the just-prepared structural bonding barrel surface quality or its bond durability. Moreover, such methods may not be compatible for localized use on the composite structures which are being bonded. Additionally, the existing techniques may not account for the potentially wide variations of the measured results on the structural bonding surface. Even a minimum of engineering data, such as surface roughness, for example, can vary greatly when the bonding surface is prepared per procedure via hand sanding methods, grit blasting and laser techniques.
Therefore, a bond surface testing apparatus and method are needed which are capable of measuring characteristics of a bonding surface via surface energies that are activated on the bonding surface and then converted into a series of complex mathematical algorithms which output a calculated quality bonding factor that is based on the three-dimensional wettability surface energies of the bonding surface and indicates whether the bonding surface is suitable for bonding.